FIG. 1 shows a conventional power supply circuit diagram for a video product, such as a liquid crystal display (LCD) panel or a LCD TV. The video product has an AC input unit connecting to city power. The AC input unit receives AC electric signals which are converted by a rectification unit consisting of a diode cluster to become pulse wave DC electric signals, which are then corrected by a power factor regulator to become stable DC electric signals. The stable DC electric signals are coupled in parallel and output to an inverter and a second transformer through a second actuation circuit. The second transformer aims to lower the voltage to output a low voltage electric signal to drive a second load. The inverter aims to boost the voltage to output a high voltage electric signal to actuate a first load. The second load includes low voltage actuated devices, such as a video signal processing circuit, speakers, and the like. The first load is a cold cathode fluorescent lamp to illuminate the display panel.
The circuit diagram for the conventional video product set forth above shows that the electricity sources share the same rectification unit and same actuation circuit. Hence, the first load and the second load are grounded together. As the second load is actuated by a low voltage electricity and must maintain a stable DC electric signal during actuation, if the electric signal are interfered with and fluctuate, the operation performance of the second load will be affected. For instance, fluctuation stripes might appear on the display plane, color becomes non-uniform, and output sound quality of the speaker drops and noises occur. Another electricity interference takes place in the inverter circuit. The inverter circuit includes a control unit to output operation frequency, as actuation unit to receive the operating frequency and divide the electric signal and output an actuation signal, and a first transformer to receive the actuation signal and transform electricity to output a high voltage signal to drive the first load. Referring to FIG. 2, while the actuation circuit is receiving the operating frequency and dividing the electric signal, charging and fluctuation of the electric signal occurs. The fluctuation of the electric signal also affects the control unit and results in unstable operating frequency and blinking on the first load.
The interference mainly is caused by the oscillation generated by the inverter during boosting of the voltage. The oscillating electric energy affects the second load and the control unit from the jointed grounding end. As a result, the second load and the control unit are affected by the electric transmission interference of the inverter. This phenomenon frequently happens to large size video products. It has a great impact to the video and audio quality of the video products.